Dept. of Radiology, University of Pittsburgh, Pittsburgh, PA, USA.
Neuroimage. 2011 Sep 1;58(1):168-76. doi: 10.1016/j.neuroimage.2011.06.010. Epub 2011 Jun 17.
Balanced steady-state free precession (bSSFP) is an attractive fMRI method at high fields due to minimal spatial distortion. To examine sensitivity and specificity of bSSFP fMRI at ultrahigh magnetic field of 9.4T, we performed high-resolution pass-band high flip-angle (16°) bSSFP fMRI with four phase cycling (PC) angles at two repetition times (TR) of 10ms and 20ms and conventional gradient-recalled-echo (GRE) fMRI with TR of 20ms on rat brain during forepaw stimulation. The sensitivity of bSSFP fMRI with TR of 20ms was higher than that of GRE fMRI regardless of PC angle. Because of magnetic field inhomogeneity, fMRI foci were changed with PC angle in bSSFP fMRI, which was more prominent when TR was shorter. Within a middle cortical layer region where magnetic field inhomogeneity was relatively small, the homogeneity of bSSFP fMRI signals was higher at shorter TR. Acquisition of baseline transition-band bSSFP images helped to identify pass- and transition-band regions and to understand corresponding bSSFP fMRI signals. Fourier analysis of the multiple PC bSSFP datasets provided echoes of multiple pathways separately, and the main echo component showed lower sensitivity and better homogeneity than the free induction decay component. In summary, pass-band bSSFP techniques would have advantages over GRE-based fMRI in terms of sensitivity, and may be a good choice for fMRI at ultrahigh fields.
平衡稳态自由进动（bSSFP）是一种在高场强下极具吸引力的 fMRI 方法，因为它的空间失真最小。为了检验超高磁场（9.4T）下 bSSFP fMRI 的灵敏度和特异性，我们在大鼠脑进行了高分辨率带通高翻转角（16°）bSSFP fMRI 研究，采用了四种相位循环（PC）角度，重复时间（TR）为 10ms 和 20ms，以及传统的梯度回波（GRE）fMRI，TR 为 20ms，在进行前爪刺激时进行。无论 PC 角度如何，20ms TR 的 bSSFP fMRI 的灵敏度都高于 GRE fMRI。由于磁场不均匀性，bSSFP fMRI 的焦点会随 PC 角度发生变化，当 TR 更短时，这种变化更为明显。在磁场不均匀性相对较小的中层皮质区域内，较短 TR 时 bSSFP fMRI 信号的均匀性更高。获取基线过渡带 bSSFP 图像有助于识别通过带和过渡带区域，并理解相应的 bSSFP fMRI 信号。对多个 PC bSSFP 数据集的傅里叶分析可以分别提供多个路径的回波，主要回波分量的灵敏度较低，但均匀性较好，优于自由感应衰减分量。总之，在灵敏度方面，带通 bSSFP 技术将优于基于 GRE 的 fMRI，可能是超高场 fMRI 的一个不错选择。
